Separate optical device for directing light from an LED

ABSTRACT

Embodiments of the present invention provide separate optical devices operable to couple to a separate LED, the separate optical device comprising an entrance surface to receive light from a separate LED when the separate optical device is coupled to the separate LED, an exit surface opposite from and a distance from the entrance surface and a set of sidewalls. The exit surface has at least a minimum area necessary to conserve brightness for a desired half-angle of light projected from the separate optical device. Furthermore, each sidewall is positioned and shaped so that at least a majority of rays having a straight transmission path from the entrance surface to that sidewall reflect to the exit surface with an angle of incidence at the exit surface at less than or equal to a critical angle at the exit surface.

RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. 119(e)to U.S. Provisional Application No. 60/756,845, entitled “OpticalDevice”, to Duong et al., filed Jan. 5, 2006, which is hereby fullyincorporated by reference herein.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to separate optical devices. Even moreparticularly, embodiments of the present invention relate to devices andmethods that increase the ability to harness light from a separate lightemitting diode (“LED”).

BACKGROUND

Light emitting diodes (“LED”) are ubiquitous in electronics. They areused in digital displays, lighting systems, computers and televisions,cellular telephones and a variety of other devices. In an LED, as in atraditional diode, extra electrons move from an N-type semiconductor toelectron holes in a P-type semiconductor. In an LED, however, photonsare released to produce light during this process. For many applicationsit is desirable to collect as much light as possible from the LED anddistribute it into a desired cone angle.

Many conventional LED devices use a dome spherical or aspheric lensformed around the LED. Generally, the distance from the lens to the domecontrols the emission cone. The T-1¾, T-5 mm or variations thereof areexamples of dome lens LEDs. However, there are several drawbacks to thisdesign. First, typical domes can only collect an f/1 acceptance angle ofthe LED die. Hence, photons emitted greater than this angle are eithertrapped within the dome due to total internal reflection (“TIR”) oremitted out the edge of the dome at a non-usable angle.

Next, the distribution of the light is highly dependent on the accuracyof the alignment between the chip and the dome. Therefore, far field andnear field distributions are often sacrificed. Third, there can besignificant non-uniformities between the near-field and far fielddistribution. Lastly, the distribution itself is not spatially uniform.

Another conventional scheme is to place a larger dome on top of the LED.Though this method does allow most if not all of the energy to get out,there are several significant drawbacks for practical applications.First, the emission cone angle is typically greater than 180 degrees.Though light is no longer trapped, energy is emitted to an angle greaterthan the original angle of the LED. Mechanical housings and such canvignette, scatter and absorb the light at the larger angles.

Moreover, since most secondary optical systems only collect an f/1 cone(a cone having a half angle of approximately 30 degrees or less), muchof the light is lost. Thirdly, since the dome is much larger than theLED die, the distribution is over a much larger area than necessary.This translates into a lower power density (or irradiance) when thelight is focused.

Another solution is to place a TIR lens over the typical dome lens tocollect all of the emitted energy and direct it into a smaller cone.This adds complexity to the system and only addresses the problem ofgetting more light into a narrower cone angle. These systems also do notaddress conservation of brightness of the source, creating a uniformpattern and maintaining the uniformity far field as well as near field.Also, adding such a TIR lens increases the size and cost of a lightingpackage as much as tenfold, rendering this solution impractical fornearly all LED applications in electronics and portable devices. Othersystems utilize elaborate TIR lens, reflective collectors and condenserlens systems. While some reflective systems that re-image the LED from adome can maintain the radiance (e.g., an ellipsoid where the LED is atone foci and the image is at the other foci), these systems areimpractical for many applications.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide separate optical devicesand methods that substantially eliminate or reduce the shortcomings ofprevious separate optical device systems and methods. For purposes ofthis disclosure a “separate optical device” is an optical device that isformed independently from the LED, but may be molded in place on top ofthe LED.

One embodiment of the present invention includes a separate opticaldevice operable to couple to an LED; the separate optical devicecomprises an entrance surface to receive light from a layer of aseparate light emitting diode when the separate optical device iscoupled to the LED, and an exit surface opposite from and a distancefrom the entrance surface. The exit surface has at least a minimum areanecessary to conserve brightness for a desired half-angle of lightemitted from the separate optical device. Furthermore, the separateoptical device can include a set of sidewalls. Each sidewall may bepositioned and shaped so that at least a majority of rays having astraight transmission path from the entrance surface to that sidewallreflect to the exit surface with an angle of incidence at the exitsurface at less than or equal to the critical angle at the exit surface.

Another embodiment of the present invention includes a separate opticaldevice operable to couple to a separate LED, the separate optical devicecomprising an entrance surface to receive light from a layer of aseparate non-circular LED when the separate optical device is coupled tothe separate non-circular LED, an exit surface opposite from and adistance from the entrance surface, and a set of sidewalls. The exitsurface, according to one embodiment, has at least a minimum areanecessary to conserve brightness for a desired half-angle of lightemitted from the separate optical device. Furthermore, each sidewall canbe positioned and shaped so that at least a portion of rays having astraight transmission path from the entrance surface to that sidewallreflect to the exit surface with an angle of incidence at the exitsurface at less than or equal to a critical angle at the exit surface.Each sidewall shape represents a superposition of multiple contouredsurfaces. The area of the exit surface, distance and sidewall shapes canbe selected to project light with a half angle of between 10 to 60degrees with at least 60% efficiency and a desired intensity profile.

Another embodiment of the present invention includes a separate opticaldevice configured to couple to a separate LED, the separate opticaldevice comprising an entrance surface to receive light from a layer of aseparate non-circular LED when the separate optical device is coupled tothe separate non-circular LED, an exit surface opposite from and adistance from the entrance surface, and a set of sidewalls. The exitsurface can have an area at least equal to a minimum area defined by n₁²A₁Ω₁/n₂ ²Ω₂, wherein Ω₁ is the effective solid angle whereby lightenters the entrance surface, Ω₂ is the effective solid angle wherebylight leaves the exit surface, A₁ is the area of the entrance surface,n₁ is the refractive index of material of the separate optical deviceand n₂ is the refractive index of the substance external to the separateoptical device. The distance between the entrance surface and exitsurface can be selected to be at least a minimum distance so that allrays with a straight transmission path from the entrance surface to theexit surface have an angle of incidence that is less than or equal to acritical angle at the exit surface. Furthermore, each sidewall can bepositioned and shaped so that at least a portion of rays having astraight transmission path from the entrance surface to that sidewallreflect to the exit surface with an angle of incidence at the exitsurface at less than or equal to the critical angle at the exit surface.Each sidewall shape can represent a superposition of multiple contouredsurfaces. The area of the exit surface, distance and sidewall shapes canbe selected to project light with a half angle of between 10 to 60degrees with at least 60% efficiency and a desired intensity profile.

Embodiments of the present invention provide a separate optical devicethat provides technical advantages over the prior art by projectinglight with a desired half-angle and intensity profile, while conservingbrightness. Embodiments of the present invention can provide, forexample, light in 10 to 60 degrees half angle (or other half angles)with 60-96% efficiency. Efficiencies can be higher than this(approaching 100%) with appropriate anti-reflection coatings on the exitsurface or lower than this.

Another advantage is that separate optical devices according toembodiments of the present invention can be much smaller (includinggreater than ten times smaller) than previous separate optical devices.

Yet another advantage is that tight arrays of separate optical devicescan be formed without or with very minimal losses.

Embodiments of the present invention provide yet another advantage byproviding for square or rectangular outputs with uniform or near uniformintensity distributions.

Embodiments of the present invention provide another advantage byreducing or eliminating the need for secondary optics to create lightwith the desired half-angle.

Embodiments of the present invention provide yet another advantage byproviding separate optical devices that can project light with a desiredaspect ratio without additional optics.

Yet another advantage provided by embodiments of the present inventionis that light can be projected with a desired shape and intensityprofile in both near and/or far field.

BRIEF DESCRIPTION OF THE FIGURES

A more complete understanding of the present invention and theadvantages thereof may be acquired by referring to the followingdescription, taken in conjunction with the accompanying drawings inwhich like reference numbers indicate like features and wherein:

FIG. 1 is a diagrammatic representation of one embodiment of an opticalsystem including a separate optical device according to an embodiment ofthe present invention;

FIG. 2 is a diagrammatic representation of a set of rays traveling froma point to surfaces at different distances from the point;

FIG. 3 provides a diagrammatic representation of a top view of aseparate optical device according to one embodiment of the presentinvention;

FIG. 4A is a diagrammatic representation of a cross-section of a modelof a separate optical device for determining sidewall shapes;

FIG. 4B is a diagrammatic representation illustrating that the facetsfor a sidewall can be defined using a computer program;

FIG. 4C is a diagrammatic representation of one embodiment of a separateoptical device with sidewalls shaped to cause TIR so that rays arereflected from the sidewalls to the exit surface;

FIG. 5 is a diagrammatic representation of one embodiment for estimatingeffective solid angle;

FIGS. 6A-6E are diagrammatic representations describing anotherembodiment for estimating effective solid angle;

FIG. 7 is a diagrammatic representation of one embodiment of an array ofseparate optical devices;

FIG. 8 is a functional diagrammatic representation of a DLP system;

FIG. 9 is a diagrammatic representation of another embodiment of aseparate optical device;

FIG. 10 is a diagrammatic representation of yet another embodiment of aseparate optical device;

FIG. 11 is a diagrammatic representation of one embodiment of stackedseparate optical devices; and

FIG. 12 is a diagrammatic representation of still another embodiment ofa separate optical device.

DETAILED DESCRIPTION

Preferred embodiments of the invention are illustrated in the FIGURES,like numerals being used to refer to like and corresponding parts of thevarious drawings.

Embodiments of the present invention provide a separate optical devicethat is coupled to an LED to direct light from the LED to an exitinterface of the separate optical device. Ideally, the separate opticaldevice is configured so that all the light entering the separate opticaldevice from the LED is transmitted out the exit interface. To this end,the exit interface can be sized to take into account principles ofconservation of radiance. The exit interface may be the minimum sizethat allows all light entering the separate optical device from the LEDto exit the exit interface, thereby combining the desire to conserveradiance with the desire to reduce size. Additionally, the sidewalls ofthe device may be shaped so that reflection or total internal reflection(“TIR”) causes light beams incident on the sidewalls to reflect towardsthe exit interface and be incident on the exit interface with an angleless than or equal to the critical angle. Consequently, light loss dueto TIR at the exit interface is reduced or eliminated. For devicesconstructed of solid dielectric materials, use of TIR provides theadvantage of lossless reflections. If the device is instead air-filled,then the sidewalls could be made of a reflective material which wouldintroduce some minor losses.

While ideally 100% of the light entering the separate optical deviceexits the exit interface, various embodiments of the present inventionmay cause lesser amounts of light to exit the exit interface while stillproviding significant improvements over prior LED separate opticaldevices. More specifically, embodiments of the present invention allowlight received from an LED to emitted from the exit surface with a conehalf angle of 10-60 degrees with approximately 50-96% efficiency (thereis approximately a 4% efficiency loss due to fresnel losses for adielectric material of 1.5 index of refraction) with a desired intensityprofile.

FIG. 1 is a diagrammatic representation of one embodiment of an opticalsystem including a separate optical device 10, an LED 15 and asupporting structure 20. LED 15 includes a light emitting portion 25,typically a compound semiconductor such as InGaN or InGaP, and asubstrate 30, such as sapphire substrate, silicon carbide (SiC)substrate or other substrate known or developed in the art. In FIG. 1,the substrate 30 is positioned as typically embodied, above the lightemitting portion 25; in another typical design, the substrate 30 may bepositioned below the light emitting portion 25. Light from LED 15 isprimarily transmitted through emitting surface 35 to separate opticaldevice 10. LED 15 can be a wire bond, flip chip or other LED known ordeveloped in the art. FIG. 1 depicts the separate optical device affixedto the exit face of LED 15. Alternatively, it may be affixed to thesubstrate 20 and fully surround the LED 15.

The thickness of LED 15 is shown much greater in comparison to separateoptical device 10 than in an actual device, for clarity.

Separate optical device 10 is formed separately from LED 15 and can becoupled to LED 15 or substrate 20 using a friction fit, optical cementor other coupling mechanism, whether mechanical, chemical, or otherwise.Preferably, separate optical device 10 is formed of a single, moldedpiece of dielectric, optically transmitting material with a single Indexof Refraction (“IOR”) “n”, such as optically transparent silicone oracrylic, though other materials can be used. Furthermore, the IOR ofseparate optical device 10 is preferably within 20% of the IOR ofsubstrate 30 (and ideally, IOR of separate optical device 10 is equal toor greater than IOR of substrate 30).

Separate optical device 10 includes an entrance surface 50 to receivelight transmitted from LED 15. Entrance surface 50, according to oneembodiment, is the same shape as LED 15 and has an edge dimensionapproximately the same size as or slightly larger than the edgedimension of emitting surface 35 of LED 15. That is, the area ofentrance surface 50 is approximately the same size as the area of LED 15that transmits light to separate optical device 10, though entrancesurface 50 may be slightly larger than LED 15 to account for tolerancesin the manufacturing process, errors in alignment of separate opticaldevice 10 and LED 15, or other factors. As an example, for a 1 mm squareLED, entrance surface 50 may be manufactured to be 1.075 mm on eachside.

Separate optical device 10 further includes exit surface 55 thatpreferably is substantially the same shape as, substantially parallel toand substantially rotationally aligned with entrance surface 50 withinthe tolerance of the manufacturing process. The area of exit surface 55can be chosen to conserve brightness for a desired half angle accordingto the conservation of radiance (sometimes called the conservation ofbrightness) equation:

$\begin{matrix}{\frac{\Phi_{2}n_{1}^{2}A_{1}\Omega_{1}}{\Phi_{1}n_{2}^{2}\Omega_{2}} = A_{2}} & \left\lbrack {{EQN}.\mspace{14mu} 1} \right\rbrack\end{matrix}$

Φ₁=light flux entering entrance surface 50;

Φ₂=light flux exiting exit surface 55, Φ₁=Φ₂ for conservation ofbrightness;

Ω₁=effective solid angle whereby light enters entrance surface 50;

Ω₂=effective solid angle whereby light leaves exit surface 55;

A₁=area of entrance surface 50;

A₂=area of exit surface 55;

n₁=refractive index of material of separate optical device;

n₂=refractive index of substance external to the exit of separateoptical device 10 (e.g., typically air or other substance).

A₂ represents the minimum surface area of exit surface 55 so thatbrightness is conserved per the above equation. Assume, for example: LED15 is a 1 mm square LED so that entrance surface 50 is approximately 1mm square, n₁=1.5, n₂=1, Ω₁=3, Ω₂=1, then A₂ must be at least 6.75 mm²to conserve radiance. While in this example the effective solid anglesare given, methods for determining Ω₁ and Ω₂ for a desired half angleare discussed below in conjunction with FIGS. 6A-6E.

A₂ according to EQN. 1 is the minimum possible size for a given outputcone angle or Emission Half Angle to conserve radiance. Consequently, toconserve radiance, A₂ should be at least the size determined from EQN 1,but may be larger. For example, A₂ may be made slightly larger tocompensate for tolerances in the manufacturing process, errors inaligning separate optical device 10 with LED 15 or other factors.

In the case where A₂ is made larger than the value determined byequation 1, flux will be conserved, but exitance (defined as flux perunit area) will be reduced from the maximum attainable value.

To save space, however, it is preferable that A₂ be as small aspossible. For example, A₂ is preferably within 5% of the minimum areaneeded to conserve radiance within 5%. If some light power (luminousflux) may be sacrificed, A₂ can be smaller than the size dictated byconservation of radiance. Furthermore, the shape of exit surface 55 maybe different than that of entrance surface 50, so long as the area meetsthe requirements discussed above.

The distance between entrance surface 50 and exit surface 55 of separateoptical device 10—referred to as the “height” herein, though thedistance may extend in other directions than the vertical—may beselected to reduce or minimize TIR of light rays traveling directly fromentrance surface 50 to exit surface 55. TIR occurs when light isincident on the surface with an angle of incidence greater that criticalangle, which is defined by:n ₁*sin(θ_(c))=n₂ sin(90)  EQN. 2

where n₁=IOR of separate optical device;

n₂=IOR of substance external to the exit of separate optical device 10(e.g., air or other substance); and

θ_(c)=the critical angle.

For example, if n₁=1.5 and n₂=1, then θ_(c=)41.81 degrees. Accordingly,the height of separate optical device 10 can be selected to limit thecritical angle of rays incident on exit surface 55 to a range betweennormal to exit surface 55 and less than or equal to the critical angle.

Referring briefly to FIGS. 2 and 3, FIG. 2 is a diagrammaticrepresentation of a set of rays traveling from point 57 incident on asurface 55 (represented as surfaces 55 a, 55 b and 55 c at differentdistances from point 57). In the example of surface 55 a, some rays(e.g., ray 56) are incident on surface 55 a at greater than the criticalangle, causing loss of light due to TIR. In the example of surface 55 b,conversely, some rays that would be incident on surface 55 c at thecritical angle or somewhat less than the critical angle (e.g., ray 57)will instead be incident on the sidewalls. Preventing loss of theserays, if desired, can cause the complexity of the sidewall design toincrease. Moreover, the additional height requires more room toaccommodate the optical device (i.e., because the optical device istaller). Finally, in the case of surface 55 c, rays at or less than thecritical angle are incident on surface 55 while rays that would begreater than the critical angle on exit surface 55 instead are incidenton the sidewalls. TIR or reflection can be used to direct the raysincident on the sidewalls to exit surface 55 as discussed below.

The limiting ray for selecting height, according to one embodiment, isthe ray that travels the longest straight line distance from entrancesurface 50 to exit surface 55 and is incident on exit surface 55 at thecritical angle. There may be more than one ray that can be selected asthe limiting ray. In a square or rectangular configuration this is theray that enters separate optical device 10 at a corner of entrancesurface 50 and travels in a straight line to the diagonally oppositecorner of exit surface 55 such that the ray would be incident on exitsurface 55 at the critical angle.

FIG. 3 provides a diagrammatic representation of a top view of aseparate optical device 10 and of limiting ray 59 for a squareconfiguration. While, in the preferred embodiment, the height ofseparate optical device 10 is selected to limit the critical angle ofrays incident on exit surface 55 to a range of between normal to exitsurface 55 and to less than or equal to the critical angle, otherheights can be selected, though the use of other heights may decreasethe efficiency of separate optical device 10. Preferably, the distancebetween the entrance surface and exit surface is within 5% of theminimum height that causes all rays with a straight transmission pathfrom the entrance surface to the exit surface to have an angle ofincidence on the exit surface at less than or equal to the criticalangle.

Returning to FIG. 1, with selected boundary conditions of the size andshape of entrance surface 50, size and shape of exit surface 55, sizeand distance between entrance surface 50 and exit surface 55, thesidewalls (e.g., sidewall 60, sidewall 65 and other sidewalls) ofseparate optical device 10 can be shaped to direct light incident on theinner side of the sidewalls to exit surface 55 to produce a desiredintensity profile. While, for most applications the desired intensityprofile is uniform or close to uniform, other distribution profiles canbe achieved by varying the height and shapes of the sidewalls. It shouldbe noted that for the case of an ideal emitter having a uniformlambertian emission pattern, and for an optical device having theminimum calculated surface area per EQUATION 1, and a uniform radiantintensity distribution at the exit face, then the etendue equationREQUIRES the distribution of the exitance at the exit face to also beuniform. If an exitance profile other than a uniform one is desired,then the output face area must be larger than that calculated withEQN. 1. In no case is it possible for any elemental area of the outputface to have a radiance greater than the radiance of the source.

Broadly speaking, the sidewall shapes are determined so that any rayincident on a sidewall is reflected to exit surface 55 and is incidenton exit surface 55 at the critical angle or less (i.e., so that there isno loss due to internal reflection at exit surface 55). This is shown inFIG. 1 by ray 70 that has angle of incidence 75 relative sidewall 65that is greater than θ_(c) so that ray 70 is reflected to exit surface55 and has an angle of incidence 80 that is less than or equal to θ_(c).While, preferably, the sidewalls are shaped so that all rays thatencounter the inner surface of the sidewalls experience total internalreflection to exit surface 55 and are incident on exit surface 55 at thecritical angle or less, other sidewall shapes that allow some loss canbe used.

FIG. 4A is a diagrammatic representation of a cross-section of a modelof a separate optical device for determining sidewall shapes. Sidewallshapes can be determined using computer-aided design. A model of thesidewall can be created in a computer-aided design package andsimulations run to determine an appropriate sidewall shape.

According to one embodiment, each sidewall can be divided into n facetswith each facet being a planar section. For example, sidewall 100 ismade of fifteen planar facets 102 a-102 o rather than a continuouscurve. The variables of each facet can be iteratively adjusted and theresulting distribution profiles analyzed until a satisfactory profile isachieved as described below. While the example of fifteen facets isused, each sidewall can be divided into any number of facets, includingmore than thirty facets.

Each facet can be analyzed with respect to reflecting a certain subsetof rays in a separate optical device. This area of interest can bedefined as an “angular subtense.” The angular subtense for a facet maybe defined in terms of the angles of rays emanating from a predefinedpoint. Preferably, the point selected is one that will give rays withthe highest angles of incidence on the facet because such rays are theleast likely to experience TIR at the facet. In a square separateoptical device, for example, this will be a point on the opposite edgeof the entrance surface.

According to one embodiment, for a selected A₁, A₂, and height, themaximum of angle 95 of any ray that will be incident on a given sidewall(e.g., sidewall 100) without being previously reflected by anothersidewall can be determined. In this example, ray 110 emanating frompoint 115 establishes the maximum angle 95 for sidewall 100. If themaximum of angle 95 is 48 degrees and there are 15 facets for sidewall100, each facet (assuming an even distribution of angular subtenses)will correspond to a 3.2 degree band of angle 95 (e.g., a first facetwill be the area on which rays emanating from point 115 with an angle 95of 0-3.2 degrees are incident, the second facet will be the area onwhich rays emanating at point 115 with an angle 95 of 3.2-6.4 degreesare incident and so on).

For each facet the exit angle, facet size, tilt angle, or otherparameter of the facet can be set so that all rays incident on the facetexperience TIR and are reflected to exit surface 55 such that they areincident on exit surface 55 with an angle of incidence of less than orequal to the critical angle. Preferably, the sidewalls are also shapedso that a ray viewed in a cross-sectional view only hits a side wallonce. However, there may be third dimension reflection from a sidewallout of plane of the section. For a full 3D analysis, a ray that strikesa first sidewall near a corner, may then bounce over to a second sidewall, adjacent to the first, and from there to the exit face. A curvefit or other numerical analysis may be performed to create a curvedsidewall shape that best fits the desired facets. In FIG. 4A, forexample, sidewall 105 is curved rather than a set of planar facets.

To optimize the variables for each facet, a simulated detector plane 120can be established. Detector plane 120 can include x number of detectorsto independently record incident power. A simulation of light passingthrough the separate optical device may be performed and the intensitydistribution as received by detector plane 120 analyzed. If theintensity distribution is not satisfactory for a particular application,the angles and angular subtenses of the facets can be adjusted, a newcurved surface generated and the simulation re-performed until asatisfactory intensity profile is reached. Additional detector planescan be analyzed to ensure that both near field and far field patternsare uniform. Alternatively, the simulation(s) can be performed using thefacets rather than curved surfaces and the surface curves determinedafter a desired intensity profile is reached. In yet another embodiment,the sidewalls can remain faceted and no curve be generated.

FIG. 4B is a diagrammatic representation illustrating that the facetsfor a sidewall can be defined using a computer program such as MicrosoftExcel (Microsoft and Excel are trademarks of Redmond, Wash.-basedMicrosoft Corporation). The graphing feature in Microsoft Excel can beused to create a graph, shown at 125, of a sidewall shape. The samegeneral shape can be used for each sidewall or different shapes fordifferent sidewalls. A separate optical device with the specifiedsidewall shape (or with a curved sidewall shape based on the specifiedfacets) can be analyzed in, for example, Zemax optical design program(Zemax is a trademark of Zemax Development Corporation of Bellevue,Wash.). A computer simulation can be conducted in Zemax to generate aray trace and an intensity and irradiance distribution profile. If theresulting intensity and irradiance profile has an unsatisfactorydistribution or the efficiency of the separate optical device is toolow, the variables of the various facets can be adjusted and thesimulations performed again. This process can be automated through theuse of a computer program to automatically adjust facet variables.

When a satisfactory efficiency and intensity profile are achieved, aseparate optical device can be formed having the specified parameters.An example of such a separate optical device is shown in FIG. 4C whichprovides a diagrammatic representation of one embodiment of separateoptical device 10 with sidewalls shaped to cause TIR so that rays arereflected from the sidewalls to the exit surface. The shape of eachsidewall, in this embodiment, is a superposition of multiple contouredsurfaces as defined by the various facets. While a curve fit isperformed for ease of manufacturability, other embodiments of thepresent invention can retain faceted sidewalls.

As described above, various boundary conditions, particularly the areaof exit surface 55, are determined for the separate optical device sothat brightness is conserved. The minimum area of exit surface 55 can bedetermined from EQN. 1 above, which relies on various effective solidangles. Typically, the effective solid angle of light is determinedbased on equations derived from sources that radiate as Lambertianemitters, but that are treated as points because the distances ofinterest are much greater than the size of the source. The observedRadiant Intensity (flux/steradian) of a Lambertian source varies withthe angle to the normal of the source by the cosine of that angle. Thisoccurs because although the radiance (flux/steradian/m²) remains thesame in all directions, the effective area of the source decreases tozero as the observed angle increases to 90 degrees. Integration of thiseffect over a full hemisphere results in a projected solid angle valueequal to π steradians.

Turning to FIG. 5, assume a sphere 130 of given radius (R) surrounds thepoint source 132. The area A₃ can be calculated as the flat, circularsurface (e.g., surface 136) that is subtended by the beam solid angle ofinterest using a radius of the circle 134 (R_(c)) that is the distancefrom the normal ray to the intersection of the spherical surface. For agiven half angle 137 of θ of the beam, R_(c) is the product of R (theradius of the sphere) and the sine of the angle θ, such thatR _(c) =R*Sin(θ)  [EQN. 3]

The area equals:A ₃ =πR _(c) ²=π(R*Sin(θ))²  [EQN. 4A]

The area A₃ is the projected area of the solid angle as it intersectsthe sphere. The area A₃ is divided by the projected area of thehemisphere (A_(h)=πR²) and the quotient is multiplied by the projectedsolid angle of the full hemisphere (equal to π) to obtain the projectedsolid angle Ω, such that:

$\begin{matrix}{\Omega = {\pi*{\left\{ {{projected}\mspace{14mu}{area}\mspace{14mu}{of}\mspace{14mu}{desired}\mspace{14mu}{solid}\mspace{14mu}{angle}} \right\}/\left( {{projected}\mspace{14mu}{area}\mspace{14mu}{of}\mspace{14mu}{hemisphere}} \right)}}} & \left\lbrack {{{EQN}.\mspace{14mu} 4}B} \right\rbrack \\\begin{matrix}{\mspace{20mu}{\Omega = {(\pi)*\left\lbrack {\left\{ {\pi\left( {R*{{Sin}(\theta)}} \right)}^{2} \right\}/\left( {\pi\; R^{2}} \right)} \right\rbrack}}} \\{= {\pi*{{Sin}^{2}(\theta)}}}\end{matrix} & \begin{matrix}\left\lbrack {{{EQN}.\mspace{14mu} 4}C} \right\rbrack \\\left\lbrack {{EQN}.\mspace{14mu} 5} \right\rbrack\end{matrix}\end{matrix}$

For entrance surface 50, θ is approximately 90 degrees, leading to aprojected solid angle of π*Sin²(90)=π, and for the desired half angle of30 degrees, the projected solid angle is π*Sin²(30)=π/2. Using thesevalues for Ω₁ and Ω₂ for EQN. 1, A₂ can be determined for the desiredhalf angle of 30 degrees.

In the above example, the effective solid angle is determined usingequations derived from a point source. These equations do not considerthe fact that LED 15 may be square, rectangular or otherwise shaped.While this method can give a good estimate of A₂, which can be lateradjusted if necessary based on empirical or computer simulation testing,other methods of determining effective solid angle can be used.

FIGS. 6A-6E describe another method for determining effective solidangle for a separate optical device that attaches to an LED that moreaccurately accounts for the square profile of the typical separate LED.FIG. 6A is a diagrammatic representation of one embodiment of anentrance face 150 and an exit face 155 of a separate optical device 160(shown in FIG. 6B) and a hypothetical target plane 156 onto which lightis projected. For purposes of further discussion, it is assumed that thecenter of entrance face 150 is at 0,0,0 in a Cartesian coordinatesystem. Target plane 156 represents the parameters of the resultingpattern (e.g., size and half angle used by other optics). According toone embodiment, the half angle at the diagonal (shown as α₁ in FIG. 6B)is the starting point. For example, if the desired light at target plane156 has a maximum half angle of 30 degrees, α₁ for a square- orrectangular-faced separate optical device is 30 degrees. The half-anglewithin separate optical device 160 (labeled β₁ and also shown in FIG.6C) can then be determined according to:n₂ Sin (α₁)=n₁ Sin (β₁)  [EQN. 6]

where n₁ is the IOR of the separate optical device;

n₂ is the IOR of the material (typically air) into which the light isprojected from the separate optical device;

θ₁ is the half angle in the LED material (typically 90 degrees);

β₁ is the desired half angle in the separate optical device.

For example, if the desired half-angle α₁ is 30 degrees, and a separateoptical device having an IOR of 1.5 is projecting into air having an IORof 1, then β₁=19.47 degrees. A similar calculation can be performed fora ray projecting from a point on the long and short sides of entrancesurface 150. For example, as shown in FIGS. 6B and 6C, α₂ and β₂ can bedetermined for a ray traveling from the center of one edge on entrancesurface 150 to the center of the opposite edge of exit surface 155. (Thecritical angle is the same at 19.47, but β₁ is not the same as β₂. β₂ isdetermined by the geoemetry of the sides and the height to the opticaldevice.)

Using the angles calculated, the location of an effective point source157 can be determined. For a square entrance face 150, of length l₁, theeffective point source will be located X=0, Y=0 and

$\begin{matrix}{Z_{eps} = \frac{l_{1}}{\sqrt{2}*{\tan\left( \beta_{1} \right)}}} & \left\lbrack {{EQN}.\mspace{14mu} 7} \right\rbrack\end{matrix}$

Where Z_(eps) is the distance the effective point source is displacedfrom the emitting surface of the LED.

The X, Y and Z distances from the effective point source 157 to pointsF₁ and F₂ can be calculated assuming F₁ intersects a sphere of unityradius according to:X _(F1)=cos(ψ₁)sin(β₁)  [EQN. 8]Y _(F1)=sin(ψ₁)sin(β₁)  [EQN. 9]Z _(F1)=cos(β₁)  [EQN. 10]X _(F2)=cos(ψ₂)  [EQN. 11]Y _(F2)=sin(β₂)  [EQN. 12]Z _(F2)=cos(β₂)  [EQN. 13]

where ψ₁ is the angle of the diagonal ray in the X-Y plane (45 degreesfor a square) and where ψ₂=90 degrees for a ray projecting from themiddle of a side parallel to the X axis as shown in FIG. 6C. A similarmethodology based on the geometries previously calculated can be used todetermine other points (e.g., for example, the location of points T₁ andT₂ can be determined based on the location of points F₁ and F₂ and thedesired half angle of light at target plane 156.)

FIG. 6D illustrates the diagonal rays and one ray from the short sideprojected onto a sphere 159 for exit face 155 and sphere 161 for targetplane 156. For exit face 155, the projection of the intersection of theedge rays at the sphere 159 onto the plane of the exit face 155, formselliptical segments. Likewise, the projection of the diffracted exitrays at the edge of the target face intersect the sphere 161. FIG. 6E,for example, points out the circular intersection of the rays lying inthe plane formed by the edge 163 of target face 156 intersecting sphere161, and the projection of that intersection onto the target plane 156.By calculating the area of each of the elliptical segments surroundingthe square of the target face, and adding that to the area of the targetface we find the total projected area of the target face the effectivesolid angle can be determined for the target plane using Eqn 4BSimilarly, by using sphere 159 and the elliptical segments formedthereon by rays, the effective solid angle for the optical device can bedetermined. For example, the total projected area is determined asdescribed above and inserted as “projected area of desired solid angle”in equation 4B.

As one illustrative example, using the above method for a half-angle of30 degrees with a square LED and output face yields an effective solidangle of 0.552 steradians to the target in air. By contrast, the use ofthe traditional circular projected area with a 30 degree half anglewould yield an effective solid angle of 0.785 steradians. When thesevalues are then used in EQUATION 1, for given IORs and flux, thetraditional (circular) calculation yields a required exit area that isundersized by about 30%. If one were to design a system using thisapproach, the applicable physics (conservation of radiance) would reducethe light output by 30% over the optimum design. Conversely, using thecorrected effective solid angle described above calculates an exit facearea that will produce 42% more light output than is achievable with thecircular calculation.

Although particular methods of determining the effective solid angle fora separate optical device are described above, any method known ordeveloped in the art can be used. Alternatively, the minimum surfacearea to conserve brightness can be determined empirically. Moreover,while the minimum surface area calculations above assume 100% of theemitting surface of the LED is emitting, in real life devices, less than100% of the emitting surface area may be emitting and the distributionmay be uneven. The calculations of the minimum area of the exit surfacecan be adjusted to account of the actual emitting area of the LED,rather the size of the entrance surface. That is, the actual emittingarea of the LED can be used as A₁.

Separate optical devices according to embodiments of the presentinvention can project light into a desired cone angle of 10-60 degreeswith a theoretical efficiency of up to 96% (meaning that 96% of thelight received from the LED is emitted in the desired half-angles with4% fresnel loss). The efficiency can be 100% without fresnel losses.Even at only 70% efficiency, embodiments of the present inventionprovide greater efficiency than other LED technologies, while alsoproducing uniform or near uniform intensity distributions at both nearand far fields.

Advantages of the present invention can easily be seen when compared toprevious LED solutions. For a straight encapsulation (e.g., a square orcube encapsulation with straight vertical sidewalls), the effectivesolid angle at the entrance and exit are the same. Assuming an index ofrefraction of 1.5 for the separate optical device material and 1 forair, approximately 66% of light does not leave the surface opposite theentrance surface due to TIR. Consequently, a straight walled separateoptical device only provides about 44% efficiency in the amount of lightemitted out the surface opposite the entrance surface. Furthermore,secondary optics are needed to shape the light into the desired halfangle.

While a dome optical device used on typical LEDs exhibits higherefficiency, there is still light loss due to TIR, and the emitted lightis distributed over the dome surface in ray patterns that are notreadily usable for most applications. Secondary collection mechanismssuch as lenses or reflectors are therefore required to shape the emittedlight into a usable angle.

Another advantage provided by embodiments of the present invention isthat multiple separate optical devices can be easily arranged into anarray that provides light in a desired angle (e.g., into an f/1 cone)with a substantially uniform intensity distribution. FIG. 7 shows oneexample of a view of an array of separate optical devices 200. Thefootprint of the entrance surfaces and exit surfaces of the separateoptical devices are shown (e.g., entrance surface 205 and exit surface210). One advantage of using an array of separate optical devices (andcorresponding array of LEDs) is that the separate optical devices makingup array 200 can be shorter in height than a single separate opticaldevice having the same combined exit surface area and entrance surfacearea. Consequently, the same amount of light can be transmitted with thesame half angle using a smaller amount of overall volumetric space.Furthermore, such a system may be more efficient overall because smallerLEDs tend to be more efficient than larger LEDs (i.e., an array ofsmaller LEDs can be more efficient than a larger LED with the same lightemitting surface area). Arrays of LEDs with corresponding separateoptical devices can be arranged to light large areas or long linearsurfaces.

Embodiments of the present invention can be used in a variety ofapplications. One potential application is in a digital light processing(“DLP”) system. In many DLP systems, the DLP chip has an acceptanceangle of somewhere between 10 and 12 degrees half angle. The area of thechip multiplied by the acceptance angle sets the etendue of the system.A lighting system that does not match this etendue is wasting light. Inprevious systems using CPCs, light from an array of multiple LEDs isdirected through dichroic filters, to a condenser optic, to anintegrating tunnel, to an imaging relay objective and then to the cone.The integrating tunnel is needed to create uniform output.

FIG. 8, on the other hand, is a functional diagrammatic representationof a DLP system 300 using separate optical devices combined with LEDs(illustrated together as 305) according to embodiments of the presentinvention. Assume the DLP system uses three arrays of 12 LEDs each (12green LEDs, 12 red LEDs and 12 blue LEDs) (the separate optical devicescombined with LEDs are represented generally at 305 and not all areshown for the sake of simplicity). Each LED can have an individualseparate optical device. For a DLP system using separate optical devicesand LEDs 305 according to the present invention rather than CPCs withLEDs, uniform light in the desired f/1 cone (represented at 310) can beprojected through the dichroic filters 315 directly to the imaging relayoptic 320 and then to DLP chip 325 within the specified acceptanceangle. Moreover, the separate optical devices can be shaped so that theprojected light has a preferred aspect ratio, such as 4:3, whileconserving luminance. This has at least two advantages. First, space issaved because separate optical devices 305 can be generally smaller thanCPCs and the distance of the transmission path is smaller as thecondenser optic and integrating tunnel are no longer needed. Moreover,the efficiency of the system is increased as there are no light lossesdue to the condenser optic and integrating tunnel.

As with DLP system 300, separate optical devices according to variousembodiments of the present invention can be used with secondarycondensing lenses at the exit face of the separate optical device oraway from the exit face of the separate optical device. According to oneembodiment, when the condenser lens is away from the exit face of theseparate optical device, the focal plane of the condenser lens can beapproximately at the exit face of the separate optical device. Thecondenser lens can be a fresnel lens of TIR and/or refraction design, orother condenser lens. The combination of separate optical device andcondenser lens allows the ability to take a Lambertian source with abroad emission solid angle (π steradians) and convert it into a narrowsolid angle (on the order of 0.1 steradians or less) while conservingradiance of the system and doing so in a very small volume.

Another potential application for embodiments of the present inventionis cell phone display lighting. Present systems typically use threeside-emitting blue LEDs with phosphor-filled encapsulant material togenerate white light. The sides of the LED are typically opaque and alarge percentage of the light generated is absorbed by the sidewalls.This results in over 50% of the light being lost to absorption. Inaddition, the index change at the interface of the encapsulant to aircreates a TIR condition for exit rays striking the interface at greaterthan the critical angle. This results in approximately 44% loss at theinterface. Separate optical devices, according to various embodiments ofthe present invention, on the other hand, can deliver up to 95% of thegenerated light to the light guide, resulting in very large systembrightness improvements.

Phosphors and other materials including nanoparticles of variousmaterials (collectively referred to simply as “phosphors” herein) arecommonly used in conjunction with various colors of LEDs to producewhite light. According to various embodiments, the LED may also becoated with a phosphor layer between the LED and the separate opticaldevice; or, a phosphor layer can be present between the separate opticaldevice and the subsequent optical element, such as a light guide; or, aphosphor coating may be imbedded in the material of the separate opticaldevice; or, other embodiments of phosphor layering as well. In the firstcase, all rays from the phosphor-coated LED can be delivered to thelight guide. In the second case, all rays from the LED can be deliveredto the phosphor layer, and light rays backscattered from the phosphorlayer can be recycled. In the third embodiment, light scattered from thephosphor is recycled back in one direction and gets refracted back tothe light guide in the other direction. Other embodiments presentsimilar opportunities for capturing and recycling scattered light fromthe phosphor.

Another potential application for embodiments of separate opticaldevices is use as a cell phone camera flash. Present systems typicallyuse LEDs with Gaussian energy distributions that produce a very brightarea in the center of the image and dark areas at the edges, causinguneven lighting of the subject matter. Moreover, the beam shape ofpresent flash units is circular, while the image captured by the CCDcamera is rectangular. Additionally, the index of refraction change atthe interface of the encapsulant to air creates a TIR condition for exitrays striking the interface at greater than the critical angle. Thisresults in losses at the interface that are a function of the exit solidangle. Separate optical devices according to embodiments of the presentinvention, on the other hand, can deliver a rectangular or square flash,with 95% of the light received by the separate optical device from theLED being provided to the image area in a uniform distribution. Thisresults in more uniform scene illumination and higher levels ofillumination from the same LED as used in traditional systems.

Another potential application for separate optical devices according toembodiments of the present invention is for liquid crystal display(“LCD”) backlighting. Traditional LCD systems use a linear array of red,green and blue LEDs. The light from the LEDs is directed into a mixinglight guide to provide uniformity of color and intensity. Typically, theLEDs have a dome placed over the LED and light is captured by ellipticalreflectors to direct the light to the light guide. While ellipticalreflectors work well for point sources, LEDs are not point sources andsome of the rays will not get to the focii inside the light guide(approximately 20% of the light is lost). Moreover, since some lightfrom a dome encapsulant is emitted at greater than 180 degrees, some ofthe light (again, approximately 20%) is absorbed by the substrate, PCBboard and other components. Furthermore, because the dome is large withrespect to the size of the cavity in the dome, a certain percentage oflight typically gets refracted (typically around 10%). Though all theselosses are relatively small, they are multiplicative. Thus, only about57% of the light originally emitted from the LED actually gets to thelight guide.

Separate optical devices according embodiments of the present invention,on the other hand, can provide up 96% of the light received from theLEDs (e.g., red, green and blue LEDs) to the light guide (assuming about4% fresnel losses) in the desired cone angle. Consequently, lower powerLEDs can be used to achieve the same results as are possible in currentsystems or more light can be delivered at the same power consumptionlevel. Indeed, in some embodiments, the light guide may not be requiredand arrays of LEDs with separate optical devices may be used to directlybacklight LCDs.

For lighting purposes (e.g., for LCDs or other applications), red, greenand blue LEDs can be used to produce white or other color balanced lightas is known in the art. An array of LEDs (e.g., one red, one blue andtwo green or other combinations) and corresponding separate opticaldevices can be used to produce white or color balanced light forillumination. According to other embodiments, a single separate opticaldevice can be coupled to an array of multiple LEDs to produce whitelight. For example, a single separate optical device can be used for atightly spaced array having one red, one blue and two green LEDs toproduce white and color balanced light.

Another potential use for separate optical devices according to variousembodiments of the present invention is in car headlights, flashlightsand other devices. The various parameters of the separate opticaldevices can be selected to provided the desired projection cone and beamprofile.

FIG. 9 is a diagrammatic representation of another embodiment of aseparate optical device 400 in which separate optical device 400 extendsdown the sides of LED 405, which fits in a cavity or empty volumedefined at the bottom of separate optical device 400. The advantage ofextending down all or a portion of the sides of LED is that light raysthat would be lost due to TIR in LED sapphire layer 415 at thesapphire/air interface may now enter separate optical device 400. Theserays can be reflected by the sidewalls of separate optical device 400 toexit interface 420 as described above (e.g., by shaping the sidewalls tocause TIR). When the sides of LED 405 also become an emitting surface,A₁ and A₂ of separate optical device 400 can be calculated to considerthe sides in addition to the top surface of LED 405 (i.e., A₁ willinclude the surface areas of entrance surface 430, 435, 440 and otherentrance surfaces, not shown). According to other embodiments, A₁ cansimply be considered for entrance surface 430 and the size of A₂calculated and then adjusted slightly to account for the additionallight entering entrance surfaces 435, 440 and other entrance surfaces.

Separate optical device 400 can be coupled to LED 405 using a polymer orother material that has a similar or identical IOR as separate opticaldevice 400. When separate optical device 400 is placed over LED 405, thepolymer or other material can act to completely fill the air spacesbetween separate optical device 400 and LED 405. If excess material ispressed out from the joint of the separate optical device 400 and LED405, the material can be removed while still fluid to retain the shapeof light directing sidewall surfaces of separate optical device 400.

Separate optical device 400 may be substantially larger than LED 405.Consequently, additional support may be required to secure it againstvibration, shock and external force. Accordingly, a mechanicalattachment device 443 (e.g., of molded plastic, metal or other material)can contact exit face 420 or other parts of separate optical device 400and attach to supporting structure 445 or the PCB board to create anormal force to keep separate optical device 400 seated against LED 405.Sideways motion can be prevented by frictional force between attachmentdevice 443 and exit face 420 or by other forces between attachmentdevice 443 and separate optical device 400. Preferably, attachmentdevice 443 has the same IOR as separate optical device 400 so that raysexiting separate optical device 400 are not deviated as they passthrough attachment device 400. In one embodiment, separate opticaldevice 400 and attachment device 430 can be a single piece, but in otherembodiments they can be separate pieces and have different IORs. Ifattachment device 430 and separate optical device 400 are separate, theycan include interlocking locating features such as bumps or ridges formore secure and accurate alignment of the devices. An attachment device443 can be used in lieu of or in addition to bonding. Attachment device443 can include a face 446 such as a lens, layer of material or otherface through which light exiting exit surface 420 passes. Consequently,attachment device can additionally act to shape or further define theoutput beam. Though attachment device 443 is shown illustratively inFIG. 9 (which shows one embodiment of separate optical device 400 with acavity into which LED 405 fits), attachment device 443 may also be usedin conjunction with other embodiments of the separate optical device andLED, including but not limited to the embodiment shown in FIG. 1 (i.e.,a flat-bottomed separate optical device 10 being coupled directly to anLED 15).

In some cases it can be desirable to have a phosphor (or other materiallayer) to create white light from LED 405. According to one embodiment,a layer of phosphor can be coated on entrance surfaces 430, 435 and 440prior to separate optical device 400 being placed over LED 405.According to other embodiments, a phosphor layer can coat exit surface420 or be embedded in any plane of separate optical device 400 or, asnoted above, the phosphor layer can be part of attachment device 443.According to yet another embodiment, a phosphor layer can be external toseparate optical device 400 with an air gap between exit surface 420 andthe phosphor layer. The sidewalls of separate optical device 400, inthis case, can be designed so that light scattered back from thephosphor layer reenters separate optical device 400 and is partially orfully recycled.

In other cases, the phosphor can be in the bonding polymer. Separateoptical device 400 can have a passage 450 running from entrance surface430 to exit surface 420. Separate optical device 400 can be placed overLED 405 with enough space for an amount of material to be injected. Thismaterial, such as a polymer infused with phosphor, can be injectedthrough flow passage 450 to bond separate optical device 400 to LED 405.A clear polymer, or material similar to the material used for themajority of separate optical device 400, can then be injected into flowpassage 450 to make separate optical device 400 solid (i.e., to fillflow passage 450).

While, as discussed above, the sidewalls of a separate optical device(e.g., separate optical device 10 and separate optical device 400) canbe shaped so that light incident on the inner surface of the sidewallsis reflected to the exit surface due to TIR, other embodiments can relyon reflection by a reflector. FIG. 10 is a diagrammatic representationof one embodiment of a separate optical device 500 coupled to an LED505. Separate optical device 500 includes an exit surface 520 and anentrance surface 530. In the example of FIG. 10, the sidewalls ofseparate optical device 500 (e.g., sidewall 540 and sidewall 545) caninclude a reflective coating 550 that can be formed of any suitablereflective material such as nickel or aluminum. The sidewall shapes canbe selected to rely on reflection from reflective coating 550 to reflectall or most rays incident on the sidewalls to exit surface 520. Whilethere may be some losses due to absorption that would not be presentusing TIR, the use of a reflective coating may be less complex from amanufacturing standpoint. Additionally, using reflective surfaceseliminates the need to have the rays strike the sidewalls at anglesgreater than the critical angle, allowing more freedom in the design ofthe sidewall shapes.

In some applications, stacked separate optical devices can be used. FIG.11 is a diagrammatic representation of one embodiment of stackedseparate optical devices including separate optical device 560 andseparate optical device 565. According to one embodiment, a layer ofphosphor (or other material as previously discussed) can be disposedbetween the exit surface of separate optical device 560 and the entrancesurface of separate optical device 565. Layer of phosphor 570 caninclude, for example, a layer of a polymer material imbedded withphosphor. The polymer material can extend beyond the edges of the exitsurface of separate optical device 560 and include attachment mechanism(e.g., legs or other mechanisms) that can attach to PCB, a supportingsubstrate or other base. In this case, the layer of polymer material ispart of an attachment device, such as that described above. In otherembodiments, other types of material or no material is disposed betweenthe separate optical devices.

According to one embodiment, separate optical device 560 can have ahigher IOR and separate optical device 565 can have a lower IOR, or viceversa. In other embodiments, separate optical device 565 and separateoptical device 560 can have the same IOR.

FIG. 12 is a diagrammatic representation of another embodiment of aseparate optical device 600. For separate optical device 600, the height(the distance between entrance surface 605 and exit surface 610) variesdepending on the skew angle θ_(s) 619 of the cross section at thatpoint. θ_(s)=0 corresponds to a cross section taken across the separateoptical device from the middle of one side to the middle of the oppositeside. This is represented at 620 while a skew angle of 45 degrees isrepresented at 622. According to one embodiment the maximum height for asquare separate optical device (e.g., determined as described above)occurs at the cross sections having θ_(s)=45+/−n*90 degrees where n isan integer. In other words, the maximum height occurs at the diagonals(represented at 622). The minimum height occurs at θ_(s)=0+/−n*90. Otherembodiments of variable height separate optical devices can also beformed.

Separate optical devices can be formed in a variety of manners. Forexample, an array of partially completed separate optical devicescomprising the sidewalls and end surface defining a cavity can be moldedin a continuous array (e.g., appearing similar to an egg crate). Thiscan be done, for example, by injection molding. The array can then beplaced over a corresponding array of LEDs and the volume inside thecavities filled with dielectric material. The sidewalls of the arrayoptionally can be coated with a reflective material. In anotherembodiment, the array can be formed by vacuum forming of a thermoplasticsheet, draw-die forming of a metallic sheet (which may be the reflectivecoating the completed separate optical device) or other suitable methodknown or developed in the art. Again, the array can be placed over thecorresponding LEDs and the cavities filled with dielectric material tocomplete the separate optical device.

In the above embodiments, the separate optical devices are molded inplace on top of the LED, but separately from the LED. In anotherembodiment, the separate optical device can be pre-molded apart from theLED using conventional molding or other techniques. In this case, theseparate optical device can include a cavity to receive the LED. The LEDand separate optical device, as described above, can be bonded togetherusing a polymer or other bonding agent, can be held together using anattachment device or can otherwise be placed in operational relationshipto each other.

While the present invention has been described with reference toparticular embodiments, it should be understood that the embodiments areillustrative and that the scope of the invention is not limited to theseembodiments. Many variations, modifications, additions and improvementsto the embodiments described above are possible. For example, thevarious ranges and dimensions provided are provided by way of exampleand optical devices according to the present invention may be operablewithin other ranges using other dimensions. It is contemplated thatthese variations, modifications, additions and improvements fall withinthe scope of the invention as detailed in the following claims.

1. A separate optical device operable to couple to a separate LED, theseparate optical device comprising: an entrance surface to receive lightfrom a separate LED when the separate optical device is coupled to theseparate LED; an exit surface opposite from and within 10% of a minimumdistance from the entrance surface so that all light rays having adirect transmission path from the entrance surface to the exit surfacewill be incident on the exit surface at less than or equal to a criticalangle at the entrance surface, wherein the exit surface has an area thatis within 10% of a minimum area necessary to fully conserve radiance fora desired half-angle of light projected from the separate opticaldevice; a set of sidewalls, wherein each sidewall has a plurality ofsections, each section based on a different curve and adapted to reflectlight having a straight transmission path to that section in acorresponding angular sub-tense to the exit surface so that the light isincident on the exit surface at less than or equal to the critical angleat the exit surface and wherein the separate optical device is shaped toemit in a uniform distribution pattern from the exit surface at least70% of the light entering the separate optical device through theentrance surface.
 2. The separate optical device of claim 1, wherein theexit surface has the minimum area necessary to conserve brightness forthe desired half-angle of light emitted from the separate opticaldevice.
 3. The separate optical device of claim 1, wherein the exitsurface has an area that is at least equal to and within 10% of aminimum area equal to$\frac{\Phi_{2}n_{1}^{2}A_{1}\Omega_{1}}{\Phi_{1}n_{2}^{2}\Omega_{2}}$wherein Φ₁ is the light flux entering the entrance surface, Φ₂ is thelight flux exiting exit surface, Ω₁ is the effective solid angle wherebylight enters the entrance surface, Ω₂ is the effective solid anglewhereby light leaves exit surface; A₁ is the area of the entrancesurface, n₁ is the refractive index of material of the separate opticaldevice and n₂ is the refractive index of the substance external to theseparate optical device.
 4. The separate optical device of claim 3,wherein the has a square emitting surface and wherein the effectivesolid angle whereby light leaves the exit surface of the separateoptical device is determined to account for the square emitting surfaceof the LED.
 5. The separate optical device of claim 1, wherein theseparate optical device is shaped to emit in the uniform distributionpattern from the exit surface at least 80% of the light entering theseparate optical device through the entrance face.
 6. The separateoptical device of claim 5, wherein each section reflects light throughtotal internal reflection.
 7. The separate optical device of claim 5,further comprising a reflective layer and wherein each sidewall isshaped so that the at least 80% of rays are reflected by the reflectivelayer to the exit surface with an angle of incidence on the exit surfaceat less than or equal to the critical angle at the exit surface.
 8. Theseparate optical device of claim 1, wherein the separate optical deviceis formed of a single piece of solid material.
 9. The separate opticaldevice of claim 8, wherein the separate optical device has an index ofrefraction within 20% of the index of refraction of a substrate of theLED.
 10. The separate optical device of claim 1, wherein the entrancesurface and exit surface have the same shape and aspect ratio as theLED.
 11. The separate optic-al device of claim 1, wherein the exitsurface is parallel to and rotationally aligned with the entrancesurface.
 12. The separate optical device of claim 1, wherein theentrance surface is square.
 13. The separate optical device of claim 1,wherein the separate optical device is configured to output asubstantially square and uniform beam of light.
 14. The separate opticaldevice of claim 1, wherein the separate optical device is configured todirect light from the LED into a smaller solid angle.
 15. The separateoptical device of claim 14, wherein the separate optical device isconfigured to provide a maximum radiant intensity.
 16. A separateoptical device operable to couple to a separate LED, the separateoptical device comprising: an entrance surface to receive light from alayer of a separate LED when the separate optical device is coupled tothe separate LED; an exit surface opposite from and a within 10% of aminimum distance from the entrance surface so that all light rays havinga direct transmission path from the entrance surface to the exit surfacewill be incident on the exit surface at less than or equal to a criticalangle at the entrance surface, wherein the exit surface has an areawithin 10% of a minimum area necessary to fully conserve radiance for adesired half-angle of light projected from the separate optical device;a set of sidewalls, wherein each sidewall has a plurality of sections,each section based on a different curve and adapted to reflect lighthaving a straight transmission path to that section in a correspondingangular sub-tense to the exit surface so that the light is incident onthe exit surface at less than or equal to the critical angle at the exitsurface and; wherein the separate optical device is shaped to project atleast 70% of the light entering the entrance surface of the separateoptical device from the exit surface with a half angle of between 10 to60 degrees a desired intensity profile.
 17. The separate optical deviceof claim 16, wherein the area of the exit surface, distance and sidewallshapes are selected to project light with a half angle of between 10 to60 degrees with at least 90% efficiency.
 18. The separate optical deviceof claim 16, wherein the exit surface has an area that is at least equalto and within 10% of a minimum area equal to Φ₂n₁ ²A₁Ω₁/Φ₁n₂ ²Ω₂ whereinΦ₁ is the light flux entering the entrance surface, Φ₂ is the light fluxexiting exit surface, Ω₁ is the effective solid angle whereby lightenters the entrance surface, Ω₂ is the effective solid angle wherebylight leaves exit surface; A₁ is the area of the entrance surface, n₁ isthe refractive index of material of the separate optical device and n₂is the refractive index of the substance external to the separateoptical device.
 19. The separate optical device of claim 18, wherein theLED has a square emitting surface and wherein the effective solid anglewhereby light leaves the exit surface is determined to account for thesquare emitting surface shape of the LED.
 20. The separate opticaldevice of claim 16, wherein the separate optical device is shaped toemit in the uniform distribution pattern from the exit surface at least80% of the light entering the separate optical device through theentrance face.
 21. The separate optical device of claim 16, wherein theseparate optical device is formed of a single piece of solid material.22. The separate optical device of claim 21, wherein the separateoptical device has an index of refraction within 20% of the index ofrefraction of the layer of the LED.
 23. The separate optical device ofclaim 16, wherein the entrance surface and exit surface have the sameshape and aspect ratio as the LED.
 24. The separate optical device ofclaim 16, wherein the exit surface is parallel to and rotationallyaligned with the entrance surface.
 25. The separate optical device ofclaim 16, wherein the entrance surface is square.
 26. A separate opticaldevice configured to couple to a separate LED, the separate opticaldevice comprising: an entrance surface to receive light from a layer ofa separate LED when the separate optical device is coupled to theseparate LED; an exit surface opposite from and a distance from theentrance surface: wherein the exit surface has an area at least equal toand within 10% of a minimum area defined by$\frac{\Phi_{2}n_{1}^{2}A_{1}\Omega_{1}}{\Phi_{1}n_{2}^{2}\Omega_{2}}$ wherein Φ₁ is the light flux entering the entrance surface, Φ₂ is thelight flux exiting exit surface, Ω₁ is the effective solid angle wherebylight enters the entrance surface, Ω₂ is the effective solid anglewhereby light leaves exit surface; A₁ is the area of the entrancesurface, n₁ is the refractive index of material of the separate opticaldevice and n₂ is the refractive index of the substance external to theseparate optical device; wherein the distance is selected to be at leastequal to and within 10% of a minimum distance so that all rays with astraight transmission path from the entrance surface to the exit surfacehave an angle of incidence that is less than or equal to a criticalangle at the exit surface; a set of sidewalls, wherein each sidewall hasa plurality of sections, each section based on a different curve andadapted to reflect light having a straight transmission path to thatsection in a corresponding angular sub-tense to the exit surface so thatthe light is incident on the exit surface at less than or equal to thecritical angle at the exit surface; and wherein the separate opticaldevice is shaped to project at least 60% of light entering the entrancesurface of the separate optical device from the exit surface with a halfangle of between 10 to 60 degrees a desired intensity profile.
 27. Theseparate optical device of claim 26, wherein the area of the exitsurface, distance and sidewall shapes are selected to project light witha half angle of between 10 to 60 degrees with at least 90% efficiency.28. The separate optical device of claim 26, wherein the area of theexit surface is within 5% of the minimum area and the distance is within5% of the minimum distance.
 29. The separate optical device of claim 26,wherein the LED has a square emission surface and wherein the effectivesolid angle whereby light leaves the exit surface is determined toaccount for the square emission surface of the LED.
 30. An opticalsystem comprising: an LED having an emitting surface; and a separateoptical device coupled to the LED, the separate optical devicecomprising an entrance surface, an exit surface and a set of sidewallsrunning from edges of the entrance surface to edges of the exit surface,wherein: the entrance surface is positioned to receive light from theemitting surface of the LED; the exit surface is opposite from andwithin 10% of a minimum distance from the entrance surface so that alllight rays having a direct transmission path from the entrance surfaceto the exit surface will be incident on the exit surface at less than orequal to a critical angle at the entrance surface, wherein the exitsurface has an area that is within 10% of a minimum area necessary tofully conserve radiance for a desired half-angle of light projected fromthe separate optical device; each sidewall has a plurality of sections,each section based on a different curve and adapted to reflect lighthaving a straight transmission path to that section in a correspondingangular sub-tense to the exit surface so that the light is incident onthe exit surface at less than or equal to the critical angle at the exitsurface; and the separate optical device is shaped to emit in a uniformdistribution pattern from the exit surface at least 70% of the lightentering the separate optical device through the entrance surface. 31.The optical system of claim 30 further comprising: a phosphor layerdisposed between an emitting surface of the LED and the entrance surfaceof the separate optical device.
 32. The optical system of claim 31,wherein the phosphor layer is selected to produce white light.
 33. Theoptical system of claim 30 further comprising: a phosphor layer disposedon the exit surface of the separate optical device.
 34. The opticalsystem of claim 33, wherein the phosphor layer is selected to producewhite light.
 35. The optical system of claim 30, further comprisingmultiple additional LEDs coupled to the separate optical device.
 36. Theoptical system of claim 30, further comprising multiple additional LEDs,each coupled to a corresponding separate optical device to form an arrayof separate optical devices.